1. Field of the Invention
This invention relates to a moving apparatus for a moving body, and particularly, to a moving apparatus for a moving body which can accomplish accurate control of the movement speed of the moving body. Such a moving apparatus is utilized, for example, for the movement of an optical head and an optical information recording medium in an optical information recording-reproducing apparatus.
2. Related Background Art
Magnetic and optical methods are known for an information recording-reproducing apparatus in which an optical information recording medium and an optical head are reciprocally moved relative to each other to thereby accomplish information recording and/or reproduction, and in recent years, attention has been paid to an optical method using a light beam.
As the types of recording media in such an optical information recording-reproducing apparatus, there are an optical disk which is a disk-like recording medium that is rotated, an optical card which is a card-like recording medium that is reciprocally moved, and an optical tape. These have their own merits and demerits and are properly used depending on the purpose, use, etc., and above all, the optical card is finding widening use because of its ease of manufacture, its good portability and its good accessibility.
Various methods of causing a light beam to scan the optical card have been conceived, and a system whereby the applied position of the light beam is linearly moved on a recording medium relative thereto and reciprocally moved, and the applied position of the beam is moved relative to the recording medium in a direction orthogonal to the reciprocal movement to thereby accomplish scanning has advantages such as simplicity of the overall mechanism and the ease with which accuracy is obtained.
However, this system suffers from problems, with respect to performance such as the inconsistent speed and vibration including the jitter resulting from the use of a timing belt and problems with respect of to cost attributable to the necessity of using a motor of high performance and the great number of parts of high accuracy. Recently, from such viewpoints, a system using a linear motor of the voice coil type as shown in FIGS. 1A and 1B of the accompanying drawings has been proposed as drive means for reciprocal movement. FIG. 1A is a cross-sectional view in a direction indicated by double-head arrow Y which is the direction of relative reciprocal movement, and FIG. 1B is a cross-sectional view in a direction indicated by double-head arrow X which is a direction perpendicular to the direction Y which is the direction of relative reciprocal movement.
In FIG. 1, a carriage 1, on which an optical card C which is an optical information recording medium is placed, has a holding mechanism 2 for the optical card C on the upper surface thereof, and slide bearings 3 provided in the lower portion thereof are slidably fitted to two slide shafts 5 fixed to an apparatus body 4 and are supported for movement in the direction Y. A voice coil 6 is mounted between the two slide shafts 5 and is adapted to move in the direction Y as a unit with the carriage 1. On the upper and lower portions of the voice coil 6, yokes 7 and 8 having their opposite ends fixed to the apparatus body 4 are disposed along the direction Y, and are coupled to iron pieces 10 and 11 with the opposite ends of a yoke 9 extending through the voice coil 6 to thereby constitute a magnetic circuit. Permanent magnets 12 and 13 are mounted on the yokes 7 and 8 in such a manner that their N or S poles are opposed to each other.
In the above-described construction, when an electric current is supplied to the voice coil 6, there is obtained a drive force in the direction Y and therefore, by reversing this electric current, reciprocal movement of the carriage 1 becomes possible. Accordingly, an optical head for effecting information recording and/or reproduction on an upper medium, not shown, is moved in the direction X and a track on the optical card C is selected and at the same time, the carriage 1 is reciprocally moved in the direction Y, whereby the medium surface of the optical card C is scanned by a light beam.
Since in the optical information recording-reproducing apparatus of this type, it is necessary to enhance the movement speed of the optical card, a linear encoder is used to effect speed servo control by a frequency/voltage converter or speed servo control by PLL (phase locked loop).
Heretofore, slide, bearings such as linear ball bearings or synthetic resin of a fluorine series have been used as the slide bearings 3 for supporting the reciprocal movement as described above. However, the linear ball bearings require the high accuracy of the slide shafts 5, and are high in cost, and the synthetic resin of the fluorine series are low in cost, but it is difficult to obtain sufficiently low frictional resistance and wear proof from them. Also, it is desirable that the weight of the carriage 1 be as light as possible to shorten the time it takes to reach a desired speed. However, in the case of light weight, it becomes difficult, due to click slip that occurs during a low speed, to enhance the gain of a speed servo system, and this leads to the problem that the speed cannot be maintained sufficiently constant. This problem that sufficiently constant speed cannot be kept, during a low speed is due to the magnitude of mechanical resistance occurring in the direction of movement of the carriage.
The carriage on which the optical card is placed has been described above as an example, and the above-noted problem likewise arises when the optical head is moved.